in reply to Re^3: Using 'each' to get random (key, value) pair from hash returns "uninitialized value"
in thread Using 'each' to get random (key, value) pair from hash returns "uninitialized value"

To the question in your previous post I would say that should work.

So would I and the line does look rather nice. Unfortunately, it doesn't seem to work as you might expect. It does look as if it is resetting the iterator but it is failing to consistently retrieve the values from the hash, only managing to get the value for key "six" twice and not getting any others.

knoppix@Microknoppix:~$ perl -Mstrict -wE '
> my %hash = (
>    one => q{ein},
>    two => q{zwei},
>    six => q{sechs},
>    );
> say qq{@{ [ %hash ] }};
> for ( 1 .. 9 )
> {
>     my ( $k, $v ) = each %hash || each %hash;
>     say qq{$_: $k => $v}
> }'
six sechs one ein two zwei
Use of uninitialized value $v in concatenation (.) or string at -e lin
+e 11.
1: six => 
Use of uninitialized value $v in concatenation (.) or string at -e lin
+e 11.
2: one => 
Use of uninitialized value $v in concatenation (.) or string at -e lin
+e 11.
3: two => 
4: six => sechs
Use of uninitialized value $v in concatenation (.) or string at -e lin
+e 11.
5: one => 
Use of uninitialized value $v in concatenation (.) or string at -e lin
+e 11.
6: two => 
7: six => sechs
Use of uninitialized value $v in concatenation (.) or string at -e lin
+e 11.
8: one => 
Use of uninitialized value $v in concatenation (.) or string at -e lin
+e 11.
9: two => 
knoppix@Microknoppix:~$

[download]

I can't puzzle out what is going on here. I wondered if it was a precedence problem but changing each %hash to each( %hash ) made no difference.

Can anyone shed any light on what's happening here?

Update: A different approach to prove to myself that the each would behave as described.

knoppix@Microknoppix:~$ perl -Mstrict -wE '
> my %hash = (
>    one => q{ein},
>    two => q{zwei},
>    six => q{sechs},
>    );
> say qq{@{ [ %hash ] }};
> my $ct;
> for ( 1 .. 3 )
> {
>     while ( my ( $k, $v ) = each %hash )
>     {
>         $ct ++;
>         say qq{$ct: $k => $v}
>     }
> }'
six sechs one ein two zwei
1: six => sechs
2: one => ein
3: two => zwei
4: six => sechs
5: one => ein
6: two => zwei
7: six => sechs
8: one => ein
9: two => zwei
knoppix@Microknoppix:~$

[download]

Cheers,

JohnGG

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Re^5: Using 'each' to get random (key, value) pair from hash returns "uninitialized value"
by jethro (Monsignor) on Jan 29, 2011 at 01:09 UTC

    It did take a while, but I finally got it. The || creates boolean, i.e. scalar context. And each() in scalar context returns only the key and not the index.

[reply]

      An excellent piece of detective work :-)

      So just grabbing the key alone and pulling the value manually will work.

      knoppix@Microknoppix:~$ perl -Mstrict -wE '
my %hash = (
   one => q{ein},
   two => q{zwei},
   six => q{sechs},
   );
say qq{@{ [ %hash ] }};
for ( 1 .. 9 )
{             
    my $k = each %hash || each %hash;
    say qq{$_: $k => $hash{ $k }};
}'
six sechs one ein two zwei
1: six => sechs
2: one => ein
3: two => zwei
4: six => sechs
5: one => ein
6: two => zwei
7: six => sechs
8: one => ein
9: two => zwei
knoppix@Microknoppix:~$

      [download]

      Thanks for clearing up the mystery.

      Update: Apologies to duelafn, I didn't see his post before making this essentially identical reply.

      Cheers,

      JohnGG

[reply]
[d/l]
        Perfect - in a way this works even better for me since I don't really need the value - just the key anyway.
        And yes thanks to all for the incredible follow through and detective work.
[reply]

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